The Fourth Amendment
The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.

Washington -- 9/11 indelibly altered America in ways that some now fear have put the government's counterterrorist strategies of domestic surveillance and data mining on a collision course with the Fourth Amendment to the Constitution and its protection of our civil liberties.

Invisibly, the country crossed a watershed in the shadow of the terrible assaults of 9/11. In their alarm over having been blindsided by the hijackers, the FBI, Justice Department, the Pentagon and the National Security Agency mounted an information-gathering stampede to try to discover hidden Al Qaeda cells in America.

"Most of us thought, based on the information at the time, that a so-called 'second-wave attack' was probably imminent," recalls Larry Mefford, assistant FBI director for counterterrorism from February 2002 to November 2003.

"There probably wasn't a week that went by that I wasn't informed of new information concerning associates of Al Qaeda or other radical extremist elements in the United States that we didn't know about the week before," Mefford explains. "That gives you a sense of the kind of insecurity we felt. The question I always asked is: What's out there that I don't yet know about?"

The government's angst about an expected second wave drove a critical shift in America's war-fighting strategy and caused a sea change inside the FBI and Justice Department. America adopted a new paradigm of war, the paradigm of pre-emption -- hitting the terrorists before they hit us.

"It was a massive cultural shift," former Attorney General John Ashcroft explains. "We had to move from that old modality of proving what happened to preventing something from happening."

That paradigm shift was embodied in President Bush's secret orders to the National Security Agency (NSA) to conduct eavesdropping inside the United States without a court warrant. It was also embodied in the new powers that Congress gave the FBI in the Patriot Act, such as broadly extending the reach of FBI administrative subpoenas, known as national security letters, to secretly obtain financial and other personal information on anyone living in America without first getting a court warrant.

Those measures, many national security lawyers said, cut against the grain of the Fourth Amendment, which protects all Americans from unreasonable searches and seizures by the government. It imposes a tough legal standard on the government, requiring "probable cause" that a targeted suspect is involved in criminal activity in order to obtain investigative warrants.

Intelligence officials such as Mefford saw the tradeoffs between greater security and protecting civil liberties. "I always said, when I was in my position running counterterrorism operations for the FBI," Mefford recalls, "how much security do you want and how many rights do you want to give up? I can give you more security but I've got to take away some rights."

These rights are protected, according to senior Justice Department attorney James Baker, by a process called "minimization" -- procedures intended to minimize the collection, analysis and distribution of information collected on innocent people not relevant to an investigation. Since 1978, that process has been overseen by a special security court, known as the Foreign Intelligence Surveillance Court, or FISA court.

But in the case of warrantless wiretapping, there is no court supervision. What's more, the whole operation is secret so the Congress, defense attorneys and the public are kept in the dark. The president's terrorist surveillance program has now been moved under the jurisdiction of the FISA court. But if there are other secret NSA surveillance programs out there -- as some have alleged -- there is no court supervision and Congress, defense attorneys and the public are kept in the dark.

Even John Yoo, the former Justice Department attorney who wrote the official legal opinions justifying the NSA eavesdropping program in 2002, concedes that warrantless domestic surveillance raises Fourth Amendment concerns.

But Yoo contends that the Constitution gives the president expanded powers in wartime to order warrantless surveillance. "We don't require a warrant, we don't require reasonable searches and seizures when the army, the military's out on the battlefield, attacking, killing members of the enemy," Yoo observes. And he argues that this becomes an even more important power of the government when an enemy such as Al Qaeda infiltrates American society to conduct attacks on our homeland.

Critics take sharp issue with this logic. The problem, they say, is that in a strategy of pre-emption, where no crime has yet been committed and where potential terrorists blend in with the rest of society, agencies like the NSA, FBI and the Department of Homeland Security often do not know precisely who they are looking for and must engage in guesswork and fishing for clues and suspects.

"When you talk about prevention, … you have to cast the net a bit more broadly and you have to start to work with situations where you are going to collect a lot of data and then try to connect the dots," explains Michael Woods, an attorney in the FBI's national security division from 1997 to 2002. "But that means you're going to end up holding a lot of data about ordinary people who have nothing to do with your threat."

Former senior CIA legal counsel Suzanne Spaulding puts the warning even more bluntly: "Our technology is not perfect, our programs are not perfect, and it is inevitable that totally innocent Americans are going to be affected by these programs."

Our FRONTLINE program showed two major pre-emption operations at work on a broad scale. One was the FBI dragnet in Las Vegas, which collected records on 250,000 fun-seeking vacationers during the run up to New Year's 2004. The other is the NSA's tapping into the massive flow of domestic as well as international Internet traffic at AT&T's offices in San Francisco, and possibly in 15 or 20 other cities around America.

In Las Vegas, the FBI did not know precisely who or what it was looking for, so it gathered masses of information to sift through. In the end, it turned out that its original tip had been wrong because some intelligence analysts had improperly decoded a suspected Al Qaeda message.

In the case of AT&T's Internet traffic, the problem is that terrorist communications are not as easy for the NSA to isolate and pluck out as President Bush suggested. In today's digital world, domestic and international calls are all mixed together. Phone calls and e-mail are broken into pieces, or packets, which travel piecemeal to their destination. Digital communications make it extremely difficult, if not impossible, to unscramble the traffic of potential terrorists from the traffic of ordinary people, without scanning it all with high-speed computers and extremely sophisticated software.

That rings alarm bells for lawyers such as Peter Swire, an Ohio State University law professor who was the White House adviser on privacy for the Clinton administration. Swire sees pre-emption measures such as dragnets and data mining as often conflicting with the letter and spirit of the Fourth Amendment, which requires individualized suspicion, firm evidence and probable cause for action.

The mindset of pre-emption, says Swire, is: "Check everybody. Everybody is a suspect. Everybody's phone records, everybody's e-mail is subject to government scrutiny, and if you're good, we won't bother you, and if you look a little strange, then you might get on a watch list."

Pre-emption sweeps not only trouble lawyers but also ordinary Americans if -- and that is a big if -- they happen to discover that they have been caught up in a government dragnet. Stephen Sprouse and Kristin Douglas of Kansas City, Mo., who happened to get married in Las Vegas when the FBI was on the hunt of terrorists there, were horrified to discover the FBI had collected their records.

Sprouse is angered that he was checked out as a potential threat. "I am innocent," he declares. "I shouldn't be bothered, pestered." His bride is no longer satisfied by the government's telling Americans not to worry, if they're innocent.

"I felt that way until I found out I was one of those people that was on the list," Douglas says. "I mean, I'm sure that the government does a lot of things that I don't know about, and I've always been okay with that -- until I found out that I was included."